1. Field of the Invention
The present invention relates to a novel suspension polymerization method which provides polymerized particles exhibiting excellent charging properties. The present invention pertains especially to a suspension polymerization method for producing a toner for use in electrophotography and the toner obtained therewith.
2. Prior art
Recently, polymerized particles utilized in the particles technology for their particle functionalities, have become increasingly important. The polymerized particles are employed in space-retention agents; lubricating agents; functional carriers; mono-disperse particles having surface activity; standardization particles; toners; and functional fillers for providing fluidity and/or polishing properties to a paint base. As the method for producing the polymerized particles, a polymerization method, a mechanical crushed method, or the like has been known. With regard to the polymerization method, in general, either an emulsion polymerization method or a suspension polymerization method may be employed.
In the conventional suspension polymerization method, polymerized particles are produced by adding a mixture composed of a monomer composition, a polymerization initiator, and the like to an aqueous medium, followed by polymerization of the mixture in the aqueous medium using a dispersing device. The advantages of the polymerized particles, obtained by the method described above, are that (1) the polymerized particles are spherical and exhibit an excellent fluidity, and (2) production of the polymerized particles is a simple and non-costly process. For this reason, it is proposed that the suspension polymerization method be applied to the production of a toner for use in electrophotography and the like, as disclosed in Japanese Patent Application Second Publication Nos. 36-10,231 and 47-51,830, and Japanese Patent Application First Publication No. 57-53,756.
In the toner for use in electrophotography, the charging properties thereof are generally controlled by dispersing a charge control agent in the toner particles. In addition, the selection of the appropriate raw materials for the toner are dependent on the system of the photocopier.
To date, the known compounds used as a negative control agent for maintaining a negative charge on the toner include a complex between a monoazo dye and a metal, a complex between salicylic acid and a metal, a salt between a salicylic acid derivative and a metal, and a complex between a metal and an azo compound including a phenylcarbamoylnaphthyl group. In addition, a nigrosine dye or a compound composed of a quaternary ammonium salt of naphthylsulfonic acid are the known compounds used as a positive charge control agent for maintaining a positive charge on the toner.
When a toner for use in electrophotography is produced by using a melt-kneading method, wherein a mixture of a binder resin, a coloring agent, and a compound such as the above-described complex, salt, or dye is mixed in a predetermined ratio, melt-kneaded and then pulverized, the resulting toner exhibits an excellent negative or positive charging property.
However, in the case of using the conventional suspension polymerization method described above, a compound such as the above-described complex, salt, or dye cannot be uniformly mixed with polymerized toner particles, resulting in a separation of the compound from the toner particles. For this reason, the polymerized toner particles cannot exhibit excellent charging properties. In addition, since a compound such as a complex, salt, or dye suitable for the suspension polymerization is not employed in the conventional suspension polymerization method, it is difficult for the toner particles to be appropriately charged.